Reduce contention on free-threaded build

[ngoldbaum]

This uses thread-local storage to avoid a scaling bottleneck due to a global cache in CPython internals. Unfortunately it's pretty slow ~10% of the total runtime of my benchmark is in the type_lookup function, I'm going to look at whether it can be faster...

Also refactors some rust code so it doesn't block other threads from doing work if the interpreter requests a GC pass.

[nascheme]

I created a bug in the cpython issue tracker: python/cpython#132380

Based on my benchmark runs, my proposed PR for 3.13 removes the need for type_lookup() function.

[nascheme]

I implemented an alternative fix for CPython, which we can also backport to Python 3.13. It adds a specialized and faster type lookup function if using a non-interned name:

python/cpython#132652

[ngoldbaum]

FWIW the latest upstream patch for this is python/cpython#133669. I think @nascheme is still planning to have a fix merged before 3.14rc1.

[zsol]

How much of this pr do you think is still useful after that patch lands in cpython?

[ngoldbaum]

The avoiding holding the GIL in the native library helps a little.

I haven't actually been able to find a way to beat multiprocessing using libcst. There's still some contention due to GC pauses.